Treatment for Electroplating Racks to Avoid Rack Metallization

ABSTRACT

An electroplating rack for supporting non-conductive substrates during an electrodeposition process is described. The electroplating rack is coated with a non-conductive material, such as a PVC plastisol. The electroplating rack is treated with a non-aqueous solution comprising a metallization inhibitor prior to the electrodeposition process to inhibit rack plate up when using etchants that do not contain chromic acid.

FIELD OF THE INVENTION

The present invention relates generally to a method of treating electroplating racks used for supporting non-conductive substrates during a metallization step.

BACKGROUND OF THE INVENTION

For many years, processes have been available to facilitate the deposition of electrodeposited metals onto plastic substrates. Typically, the process involves the steps of:

-   -   1) Etching the plastic in a suitable etching solution such that         the surface of the plastic becomes roughened and wetted so that         the subsequently applied deposit has good adhesion;     -   2) Activating the surface of the plastic using a colloidal or         ionic solution of a metal (usually palladium) capable of         initiating the deposition of an autocatalytically applied metal         coating (e.g., copper or nickel);     -   3) Depositing a thin layer of autocatalytically applied metal;         and     -   4) Carrying out electrodeposition of metal onto the metallized         plastic substrate.         Typically, layers of copper, nickel and/or chromium will be         applied to produce the finished article.

The most widely used plastic substrates are acrylonitrile/butadiene/styrene copolymers (ABS) or ABS blended with polycarbonate (ABS/PC). These materials are readily formed into components by the process of injection molding. ABS comprises a relatively hard matrix of acrylonitrile/styrene copolymer and the butadiene polymerizes to form a separate phase. It is this softer phase of polybutadiene (which contains double bonds in the polymer backbone) which may be readily etched using various techniques.

Traditionally, the etching has been carried out using a mixture of chromic and sulfuric acids operated at elevated temperature. The chromic acid is capable of dissolving the polybutadiene phase of the ABS by oxidation of the double bonds in the backbone of the polybutadiene polymer, which has proven to be reliable and effective over a wide range of ABS and ABS/PC plastics. However, the use of chromic acid has become increasingly regulated because of its toxicity and carcinogenic nature. For this reason, there has been considerable research into other means of etching ABS plastics and a number of approaches have been suggested to achieve this.

For example, acidic permanganate is capable of oxidizing the double bonds in the polybutadiene. Chain scission can then be achieved by further oxidation with periodate ions. Ozone is also capable of oxidizing polybutadiene. However, ozone is extremely dangerous to use and highly toxic. Likewise, sulfur trioxide can be used to etch ABS, but this has not been successfully achieved on a typical plating line. Other examples of techniques for etching ABS plastics are described in U.S. Pat. Pub. No. 2005/0199587 to Bengston, U.S. Pat. Pub. No. 2009/0092757 to Sakou et al., and U.S. Pat. No. 5,160,600 to Gordhanbai et al., the subject matter of each of which is herein incorporated by reference in its entirety.

More recently, it has been discovered that ABS and ABS/PC plastic can be etched in a solution containing manganese(III) ions in strong sulfuric acid as described in U.S. Pat. Pub. No. 2013/0186774 to Pearson et al., the subject matter of which is herein incorporated by reference in its entirety.

In order to plate plastic components, they are attached to plating racks which transmit the electrical current to the sensitized and metallized plastic components. The racks are typically at least partially coated with a non-conductive material to prevent the rack from being entirely covered with metal during the electroplating process, and the most common rack coating is a PVC plastisol. The use of chromic acid in the etching stage prior to activation is effective in modifying the surface of the plastisol coating so that it is resistant to metallization after being coated with a palladium activator (usually a colloid of palladium and tin). When chromic acid is replaced with other etching techniques, for example, using processes containing permanganate or manganese (III), the plastisol coating of the plating rack becomes coated with the activator and subsequently becomes coated with a layer of either nickel or copper in the electroless plating stage. Thus, a major problem with all of the currently known methods that do not utilize chromic acid is that rack coatings tend to become plated in the subsequently electroless plating stage. This phenomenon is known as “rack plate up” and is a major problem with any form of chrome-free etching technology.

SUMMARY OF THE INVENTION

It is an object of the present invention to inhibit rack plate up in the process of electroplating non-conductive substrates.

It is another object of the present invention to inhibit rack plate up in the process of electroplating non-conductive substrates in which the non-conductive substrates are etched using a chrome-free etchant.

It is still another object of the present invention to provide a treatment for electroplating racks used for supporting non-conductive substrates during the electroplating process.

To that end, in one embodiment, the present invention relates generally to an electroplating rack for supporting non-conductive substrates during an electrodeposition process,

wherein the electroplating rack is at least partially coated with a non-conductive material; and

wherein the electroplating rack is treated with a non-aqueous solution comprising a metallization inhibitor.

In another embodiment, the present invention relates generally to a method of treating an electroplating rack used for supporting non-conductive substrates during an electrodeposition process, wherein the electroplating rack is at least partially coated with a non-conductive material, the method comprising:

contacting the electroplating rack with a non-aqueous solution comprising a metallization inhibitor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention allows for the treatment of electroplating racks used for the purpose of supporting non-conductive substrates during a metallization step. The method described herein allows for the effective activation of plastics that have been etched without the use of chromic acid while avoiding the common problem of rack “plate up” which occurs when chromic acid free etchants are used for the initial roughening of the plastic. In addition, the present invention relates generally to the catalysis and subsequent metallization of plastics such as ABS and ABS/PC plastics that have been etched in process solutions that do not contain chromic acid and without problems of “plate up” on at least partially coated racks.

In one preferred embodiment, the method generally comprises the steps of:

-   -   1) Immersing a rack partially coated with non-conductive         material in a solution containing a metallization inhibitor;     -   2) Rinsing and drying the rack;     -   3) Mounting the parts to be metallized on the rack;     -   4) Etching the plastic components mounted on the treated racks         in etching solutions that do not contain chromic acid         (including, for example, etching solutions based on permanganate         or manganese (III);     -   5) Activating the surface of the plastic by immersing the         plating racks in a solution comprising colloidal palladium/tin         or ionic palladium;     -   6) Immersing the rack in an accelerating process to remove         protective tin oxides from the surface (in the case of colloidal         palladium/tin activation) or immersing the rack in a reducing         process to form palladium metal on the surface (in the case of         ionic palladium);     -   7) Immersing the racks containing the etched and activated parts         in a metallization bath to chemically deposit either nickel or         copper onto the surface of the activated part; and     -   8) Electroplating the parts, typically by plating copper, nickel         and/or chromium.

Thus, in one embodiment, the present invention relates generally to an electroplating rack for supporting non-conductive substrates during an electrodeposition process,

wherein the electroplating rack is at least partially coated with a non-conductive material; and wherein the electroplating rack is treated with a non-aqueous solution comprising a metallization inhibitor.

As described herein, the electroplating rack is typically coated with a PVC plastisol, or another non-conductive material.

The non-aqueous solution generally comprises about 5 g/L to about 40 g/L of the metallization inhibitor, more preferably about 15 g/L to about 25 g/L of the metallization inhibitor, and most preferably about 10 g/L to about 20 g/L of the metallization inhibitor.

The non-aqueous solution is preferably maintained at a temperature of between about 25° C. and about 75° C., more preferably a temperature of between about 35° C. and about 65° C., during the time that the electroplating rack is immersed in the non-aqueous solution. In addition, the electroplating rack is immersed in the non-aqueous solution for a period of time sufficient to treat the PVC plastisol coated rack to avoid rack plate on. That is the electroplating rack is preferably immersed in the non-aqueous solution for between about 1 minute and about 60 minutes, more preferably for between about 2 minute and about 30 minutes.

The inventors of the present invention have found that metallization inhibitors that are substantially soluble in aqueous media are unsuitable for the process described herein because they tend to slowly leach into subsequent process solutions and prevent metallization of the parts. Preferably, the metallization inhibitor is at least essentially insoluble in aqueous media. Thus, the solution containing the metallization inhibitor is a non-aqueous solution.

Suitable water insoluble metallization inhibitors are generally organic compounds comprising sulfur in a −2 valency and include, but are not limited to, transition metal salts of di-substituted dithiocarbamates and tetra-substituted thiuram sulfides. Suitable dithiocarbamates include, for example, zinc dimethyl-dithiocarbamate (ZDMC), zinc diethyldithiocarbamate (ZDEC), zinc dibutyldithiocarbamate (ZDBC), zinc ethylphenyldithiocarbamate (ZEPC), zinc dibenzyldithiocarbamate (ZBEC), zinc pentamethylenedithiocarbamate (Z5MC), tellurium diethyldithiocarbamate, nickel dibutyl dithiocarbamate, nickel dimethyldithiocarbamate, and zinc diisononyldithiocarbamate. Preferred tetra-substituted thiuram sulfides include, for example, tetrabenzylthiuram disulfide, mercaptobenzothiazoles, mercaptothiazolines, mercaptobenzimidazoles, mercaptoimidazoles, mercaptobenzoxazoles, mercaptothiazole, mercaptotriazole, dithiocyanuric acid, and trithiocyanuric acid. Combinations of one or more of the metallization inhibitors may also be sued. In a preferred embodiment, the metallization inhibitor comprises nickel dibutyl dithiocarbamate or tetrabenzylthiuram disulfide.

Suitable non-aqueous solvents include, but are not limited to butylene carbonate, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, propyl lactate, gamma-butyrolactone, ethyl 3-ethoxypropionate and diethyleneglycol monomethyl ether acetate, ethyleneglycol monomethyl ether acetate, ethyleneglycol monoethyl ether acetate, diethyleneglycol monoethyl ether acetate, diethyleneglycol mono-n-butyl ether acetate, propyleneglycol monomethyl ether acetate, propyleneglycol monoethyl ether acetate, propyleneglycol monopropyl ether acetate, propyleneglycol monobutyl ether acetate, dipropyleneglycol monomethyl ether acetate, dipropyleneglycol monoethyl ether acetate, glycol diacetate, by way of example and not limitation.

The solvent mixture must be capable of dissolving an effective amount of the metallization inhibitor, be readily rinsed off treated racks, and be preferably non-volatile and safe to handle with regards to its toxicology and flammability. In addition, the solvent mixture should cause no damage to the rack coating. It has been found that solvents that are very readily water-soluble can have difficulty in dissolving water-insoluble metallization inhibitors and thus do not give an effective inhibition of metallization. However, substantially water insoluble solvents that readily dissolve the inhibitors and provide a better degree of inhibition can cause a greater degree of attack on the rack coating and are also more problematic to rinse off the rack after treatment.

The degree of attack on the rack coating is related to the degree of diffusion of the metallization inhibitor into the surface of the rack coating, and the choice of solvents is therefore critical to the success of the process.

The metallization inhibitor described herein can be readily applied to racks during the normal treatment cycle to remove unwanted metallic deposits from the tips of the contact points.

The invention will now be illustrated with reference to the following non-limiting examples:

Comparative Example 1

An ABS test panel and a new PVC plastisol coated test piece were processed through a standard pretreatment sequence comprising the following stages:

-   -   1) Etch the test pieces in a solution containing 400 g/L of         chromic acid, 350 g/L of sulfuric acid and 0.1 g/L of         perfluorooctylsulfonic acid (8 minutes at 65° C.);     -   2) Rinse;     -   3) Subject the test pieces to a reducing stage comprising an         aqueous solution of hydroxylamine hydrochloride and hydrochloric         acid;     -   4) Rinse;     -   5) Immerse the test pieces in a solution of 30% hydrochloric         acid as a pre-dip before activation;     -   6) Immerse the test pieces in a conventional palladium/tin         activator (MacDermid Macuplex D34C) for 3 minutes at 30° C.;     -   7) Rinse;     -   8) Immerse the test pieces in a conventional accelerator         solution (MacDermid Ultracel 9369) for 2 minutes at 50° C.;     -   9) Rinse; and     -   10) Immerse the test pieces in an electroless nickel process         designed for plating on plastic applications (MacDermid Macuplex         J64) for 7 minutes at 30° C.

Following this treatment, the test pieces were examined. It was found that the ABS test panel was fully covered in electroless nickel with no apparent voids. Subsequent electroplating of this test panel gave full coverage and good adhesion. The PVC plastisol coated test piece showed no coverage of the electroless nickel. Repeated cycling of ABS and PVC test pieces through steps 1-10 continually showed full electroless nickel coverage of ABS and no electroless nickel coverage of the PVC.

Comparative Example 2

An ABS test panel and a new PVC plastisol coated test piece were processed through a pretreatment sequence comprising the following stages:

-   -   1) Immerse the test pieces in a solvent predip comprising 100         mL/L of propylene carbonate and 50 mL/L of gamma-butyrolactone         for 2 minutes at 35° C.;     -   2) Rinse;     -   3) Etch the test pieces in a solution comprising 12.5 M sulfuric         acid containing 0.04 M manganous sulfate and 0.02 M of         manganese(III) ions at 68° C. for 20 minutes;     -   4) Rinse;     -   5) Subject the test pieces to a reducing stage comprising an         aqueous solution of ascorbic acid; and     -   6) Carry out stages 4 to 10 of Comparative Example 1.

Following this treatment, the test pieces were examined. It was found that the ABS test panel was fully covered in electroless nickel with no apparent voids. Subsequent electroplating of this test panel gave full coverage and good adhesion. The PVC plastisol coated test piece showed significant coverage of the electroless nickel which was observed to cover between 10% and 50% of the surface area. This would be expected to cause considerable problems in commercial practice. Repeated cycling of ABS and PVC plastisol coated test pieces through steps 1-6 continually showed full electroless nickel coverage of ABS and increasing amounts of electroless nickel coverage of the PVC plastisol coated test piece.

Comparative Example 3

An old PVC plastisol coated test piece which had been cycled hundreds of times in a production facility using hexavalent chromium treatment solutions, was leached for several hours in hot water to remove any remaining hexavalent chromium on the surface (the inventors have determined that this leaching effectively eliminates any metallization inhibition provided by hexavalent chromium in the PVC plastisol).

An ABS test panel and the old PVC plastisol coated test piece were processed through stages 1-6 of Comparative Example 2.

Following this treatment, the test pieces were examined. The ABS test panel was fully covered in electroless nickel with no apparent voids. Subsequent electroplating of this test panel gave full coverage and good adhesion. The PVC plastisol coated test piece showed full coverage of the electroless nickel over the entire surface of the plastisol test piece. This would be totally unacceptable in commercial practice.

Comparative Example 4

A new PVC plastisol coated test piece was treated as follows:

-   -   A. Immerse the plastisol coated test piece in gamma         butyrolactone for 10 minutes at 65° C.;     -   B. Rinse and dry the test piece.

An ABS test panel and the treated PVC plastisol coated test piece were processed through the following stages:

-   -   1) Immerse the test pieces in a solvent predip comprising 100         mL/L of propylene carbonate and 50 mL/L of gamma-butyrolactone         for 2 minutes at 35° C.;     -   2) Rinse;     -   3) Etch the test pieces in a solution comprising 12.5 M sulfuric         acid containing 0.04 M manganous sulfate and 0.02 M of         manganese(III) ions at 68° C. for 20 minutes;     -   4) Rinse;     -   5) Subject the test pieces to a reducing stage comprising an         aqueous solution of ascorbic acid; and     -   6) Carry out stages 4 to 10 of Comparative Example 1.

Following this treatment, the test pieces were examined. It was found that the ABS test panel was fully covered in electroless nickel with no apparent voids. Subsequent electroplating of this test panel gave full coverage and good adhesion. The PVC plastisol coated test piece showed significant coverage of the electroless nickel which was observed to cover between 10% and 50% of the surface area. There was no apparent difference observed between the PVC plastisol coated test piece that had been treated in a solvent versus a PVC plastisol coated test piece that had not been treated in a solvent.

These comparative examples illustrate the problems associated with rack plate-up when chrome-free pretreatment sequences are utilized and demonstrate that old used PVC plastisol surfaces are more prone to metallization than new PVC plastisol surfaces when hexavalent chromium is absent. Comparative Example 4 demonstrates that a solvent treatment without the inhibitor has no effect.

Example 1

A new PVC plastisol coated test piece was treated as follows:

-   -   A. Immerse the plastisol coated test piece in a solution of         gamma butyrolactone containing 20 g/L of nickel         dibutyldithiocarbamate for 10 minutes at 65° C.;     -   B. Rinse and dry the test piece.

An ABS test panel and the treated PVC plastisol coated test piece were processed through the following stages:

-   -   1) Immerse the test pieces in a solvent predip comprising 100         mL/L of propylene carbonate and 50 mL/L of gamma-butyrolactone         for 2 minutes at 35° C.;     -   2) Rinse;     -   3) Etch the test pieces in a solution comprising 12.5 M sulfuric         acid containing 0.04 M manganous sulfate and 0.02 M of         manganese(III) ions at 68° C. for 20 minutes;     -   4) Rinse;     -   5) Subject the test pieces to a reducing stage comprising an         aqueous solution of ascorbic acid; and     -   6) Carry out stages 4 to 10 of Comparative Example 1.

Following this treatment, the test pieces were examined. It was found that the ABS test panel was fully covered in electroless nickel with no apparent voids. Subsequent electroplating of this test panel gave full coverage and good adhesion. In addition, the PVC plastisol coated test piece showed no coverage of the electroless nickel.

Repeated cycling of ABS and the treated PVC plastisol test piece through steps 1-6 continually showed full electroless nickel coverage of ABS and no electroless nickel coverage of the treated PVC plastisol coated test piece up to 3 cycles. After 3 cycles, approximately 10% of metallization was visible on the PVC plastisol. At this stage, the PVC plastisol coated test piece was treated in the inhibitor solution for a second time and then repeatedly cycled through stages 1 through 6 again. No metallization was found on the treated PVC plastisol for at least another 3 cycles, while full electroless nickel coverage was obtained on the ABS test piece. The appearance of the PVC plastisol was still satisfactory with little or no change from its original appearance.

Example 2

A new PVC plastisol coated test piece was treated as follows:

-   -   A. Immerse the plastisol coated test piece in a solution of         ethyl 3-ethoxypropionate containing 20 g/L of nickel         dibutyldithiocarbamate for 30 minutes at 42° C.;     -   B. Rinse and dry the test piece.

An ABS test panel and the treated PVC plastisol coated test piece were processed through stages 1-6 as described in Example 1.

Following this treatment, the test pieces were examined. It was found that the ABS test panel was fully covered in electroless nickel with no apparent voids. Subsequent electroplating of this test panel gave full coverage and good adhesion. The treated PVC plastisol coated test piece showed no coverage of the electroless nickel.

Repeated cycling of the ABS and treated PVC plastisol coated test pieces through steps 1-6 as described in Example 1 continually showed full electroless nickel coverage of ABS and no electroless nickel coverage of the treated PVC plastisol up to 4 cycles.

The appearance of the PVC plastisol was still satisfactory but was softer than the original coating.

Example 3

A new PVC plastisol coated test piece was treated as follows:

-   -   A. Immerse the plastisol coated test piece in a solution of         n-propyl lactate and ethyl 3-ethoxypropionate containing 10 g/L         of tetrabenzylthiuram disulfide for 10 minutes at 40° C.;     -   B. Rinse and dry the test piece.

An ABS test panel and the treated PVC plastisol coated test piece were processed through stages 1-6 as described in Example 1.

Following this treatment, the test pieces were examined. It was found that the ABS test panel was fully covered in electroless nickel with no apparent voids. Subsequent electroplating of this test panel gave full coverage and good adhesion. The treated PVC plastisol coated test piece showed no coverage of the electroless nickel.

Repeated cycling of the ABS and treated PVC plastisol coated test pieces through steps 1-6 described in Example 1 continually showed full electroless nickel coverage of ABS and no electroless nickel coverage of the treated PVC plastisol up to 6 cycles. After 6 cycles, a small amount of metallization was visible on the PVC plastisol. At this stage, the PVC plastisol coated test piece was treated in the inhibitor solution for a second time and then repeatedly cycled through steps 1 to 6 as described in Example 1 again. No metallization was found on the PVC plastisol for at least another 6 cycles, while full electroless nickel coverage was obtained on the ABS test piece.

The appearance of the PVC plastisol was still satisfactory, with little or no change from its original appearance.

Example 4

A new PVC plastisol coated test piece was treated as follows:

-   -   A. Immerse the plastisol coated test piece in a solution of         ethyl 3-ethoxypropionate containing 10 g/L of tetrabenzylthiuram         disulfide for 30 minutes at 40° C.;     -   B. Rinse and dry the test piece.

An ABS test panel and the treated PVC plastisol coated test piece were processed through stages 1-6 as described in Example 1.

Following this treatment, the test pieces were examined. It was found that the ABS test panel was fully covered in electroless nickel with no apparent voids. Subsequent electroplating of this test panel gave full coverage and good adhesion. The treated PVC plastisol coated test piece showed no coverage of the electroless nickel.

Repeated cycling of the ABS and treated PVC plastisol coated test pieces through steps A and B above and then through steps 1-6 as described in Example 1 (i.e. with the PVC plastisol being treated in the inhibitor solution prior to each etch and metallization cycle) continually showed full electroless nickel coverage of ABS and none or minimal electroless nickel coverage of the treated PVC plastisol up to 10 cycles. After 10 cycles, a small amount of metallization was visible on the PVC plastisol.

The appearance of the PVC plastisol was satisfactory, but was softer than the original coating.

Example 5

An old plastisol test piece which had been cycled hundreds of times on a production facility using hexavalent chromium treatment solutions, was leached for several hours in hot water to remove any remaining hexavalent chromium on the surface.

The old PVC plastisol coated test piece was treated as follows:

-   -   A. Immerse the plastisol coated test piece in a solution of         n-propyl lactate and ethyl 3-ethoxypropionate containing 10 g/L         of tetrabenzylthiuram disulfide for 5 minutes at 40° C.;     -   B. Rinse and dry the test piece.

An ABS test panel and the treated PVC plastisol coated test piece were processed through stages 1-6 as described in Example 1.

Following this treatment, the test pieces were examined. It was found that the ABS test panel was fully covered in electroless nickel with no apparent voids. Subsequent electroplating of this test panel gave full coverage and good adhesion. The treated PVC plastisol coated test piece showed no coverage of the electroless nickel despite being a very well used and aged coating with a cracked and roughened surface.

Repeated cycling of the ABS and treated PVC plastisol coated test pieces through step A and B above and then through steps 1-6 as described in Example 1 (for this example, the plastisol coating was treated in the inhibitor solution prior to each etch and metallization cycle) continually showed full electroless nickel coverage of ABS and no electroless nickel coverage of the treated PVC plastisol up to 25 cycles.

Example 6

A new PVC plastisol coated test piece was treated as follows:

-   -   A. Immerse the plastisol coated test piece in a solution of         n-propyl lactate and ethyl 3-ethoxypropionate containing 10 g/L         of tetrabenzylthiuram disulfide for 2 minutes at 40° C.;     -   B. Rinse and dry the test piece.

An ABS test panel and the treated PVC plastisol coated test piece were processed through stages 1-6 as described in Example 1.

Following this treatment, the test pieces were examined. It was found that the ABS test panel was fully covered in electroless nickel with no apparent voids. Subsequent electroplating of this test panel gave full coverage and good adhesion. The treated PVC plastisol coated test piece showed no coverage of the electroless nickel.

Repeated cycling of the ABS and treated PVC plastisol coated test pieces through steps A and B above and then through steps 1-6 as described in Example 1 (for this example, the plastisol coating was treated in the inhibitor solution prior to each etch and metallization cycle) continually showed full electroless nickel coverage of ABS and no electroless nickel coverage of the treated PVC plastisol up to 25 cycles.

The appearance of the PVC plastisol was still satisfactory, with little or no change from its original appearance. 

What is claimed is:
 1. An electroplating rack for supporting non-conductive substrates during a plating process, wherein the electroplating rack is at least partially coated with a non-conductive material; and wherein the electroplating rack is treated with a non-aqueous solution comprising a metallization inhibitor.
 2. The electroplating rack according to claim 1, wherein the electroplating rack is at least partially coated with a PVC plastisol.
 3. The electroplating rack according to claim 1, wherein the metallization inhibitor is at least substantially insoluble in aqueous media.
 4. The electroplating rack according to claim 3, wherein the metallization inhibitor is an organic compound comprising sulfur in a −2 valency.
 5. The electroplating rack according to claim 3, wherein the metallization inhibitor comprises a transition metal salt of a di-substituted dithiocarbamate or a tetra-substituted thiuram sulfide.
 6. The electroplating rack according to claim 5, wherein the metallization inhibitor is selected from the group consisting of zinc dimethyl-dithiocarbamate, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, zinc ethylphenyldithiocarbamate, zinc dibenzyldithiocarbamate, zinc pentamethylenedithiocarbamate, tellurium diethyldithiocarbamate, nickel dibutyl dithiocarbamate, nickel dimethyldithiocarbamate, zinc diisononyldithiocarbamate, tetrabenzylthiuram disulfide, mercaptobenzothiazole, mercaptothiazo line, mercaptobenzimidazole, mercaptoimidazole, mercaptobenzoxazole, mercaptothiazole, mercaptotriazole, dithiocyanuric acid, trithiocyanuric acid, and combinations of one or more of the foregoing.
 7. The electroplating rack according to claim 6, wherein the metallization inhibitor comprises nickel dibutyl dithiocarbamate or tetrabenzylthiuram disulfide.
 8. The electroplating rack according to claim 1, wherein the non-aqueous solution comprises a non-aqueous solvent, wherein the non-aqueous solvent is non-volatile and is capable of dissolving an effective amount of the metallization inhibitor.
 9. The electroplating rack according to claim 8, wherein the non-aqueous solvent is selected from the group consisting of butylene carbonate, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, propyl lactate, gammabutyrolactone, ethyl 3 -ethoxypropionate and diethyleneglycol monomethyl ether acetate, ethyleneglycol monomethyl ether acetate, ethyleneglycol monoethyl ether acetate, diethyleneglycol monoethyl ether acetate, diethyleneglycol mono-n-butyl ether acetate, propyleneglycol monomethyl ether acetate, propyleneglycol monoethyl ether acetate, is propyleneglycol monopropyl ether acetate, propyleneglycol monobutyl ether acetate, dipropyleneglycol monomethyl ether acetate, dipropyleneglycol monoethyl ether acetate, glycol diacetate, and combinations of one or more of the foregoing.
 10. The electroplating rack according to claim 9, wherein the non-aqueous solvent comprises ethyl 3-ethoxypropionate, n-propyl lactate, gamma-butyrolactone, or combinations of one or more of the foregoing.
 11. A method of treating an electroplating rack used for supporting non-conductive substrates during a plating process, wherein the electroplating rack is at least partially coated with with PVC plastisol, the method comprising: a) contacting the electroplating rack with a non-aqueous solution comprising a metallization inhibitor; b) mounting non-conductive substrates to the electroplating rack that has been contacted with the non-aqueous solution comprising a metallizaton inhibitor; and c) etching the non-conductive substrates supported on the electroplating rack with an etchant that does not contain chromic acid.
 12. (canceled)
 13. The method according to claim 11, wherein the electroplating rack is contacted with the non-aqueous solution by immersing the electroplating rack in the non-aqueous solution.
 14. The method according to claim 11, wherein the metallization inhibitor is at least substantially insoluble in aqueous media.
 15. The method according to claim 14, wherein the metallization inhibitor is an organic compound comprising sulfur in a −2 valency.
 16. The method according to claim 14, wherein the metallization inhibitor comprises a transition metal salt of a di-substituted dithiocarbamate or a tetra-substituted thiuram sulfide.
 17. The method according to claim 16, wherein the metallization inhibitor is selected from the group consisting of zinc dimethyl-dithiocarbamate, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, zinc ethylphenyldithiocarbamate, zinc dibenzyldithiocarbamate, zinc pentamethylenedithiocarbamate, tellurium diethyldithiocarbamate, nickel dibutyl dithiocarbamate, nickel dimethyldithiocarbamate, zinc diisononyldithiocarbamate, tetrabenzylthiuram disulfide, mercaptobenzothiazole, mercaptothiazoline, mercaptobenzimidazole, mercaptoimidazole, mercaptobenzoxazole, mercaptothiazole, mercaptotriazole, dithiocyanuric acid, trithiocyanuric acid, and combinations of one or more of the foregoing.
 18. The method according to claim 17, wherein the metallization inhibitor comprises nickel dibutyl dithiocarbamate or tetrabenzylthiuram disulfide.
 19. The method according to claim 11, wherein the non-aqueous solution comprises a non-aqueous solvent, wherein the non-aqueous solvent is non-volatile and is capable of dissolving an effective amount of the metallization inhibitor.
 20. The method according to claim 19, wherein the non-aqueous solvent is selected from the group consisting of butylene carbonate, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, propyl lactate, gamma-butyrolactone, ethyl 3-ethoxypropionate and diethyleneglycol monomethyl ether acetate, ethyleneglycol monomethyl ether acetate, ethyleneglycol monoethyl ether acetate, diethyleneglycol monoethyl ether acetate, diethyleneglycol mono-n-butyl ether acetate, propyleneglycol monomethyl ether acetate, propyleneglycol monoethyl ether acetate, propyleneglycol monopropyl ether acetate, propyleneglycol monobutyl ether acetate, dipropyleneglycol monomethyl ether acetate, dipropyleneglycol monoethyl ether acetate, glycol diacetate, and combinations of one or more of the foregoing.
 21. The method according to claim 20, wherein the non-aqueous solvent comprises ethyl 3-ethoxypropionate, n-propyl lactate, gamma-butyrolactone, or combinations of one or more of the foregoing.
 22. The method according to claim 11, wherein the non-aqueous solution comprises about 5 g/L to about 40 g/L of the metallization inhibitor.
 23. The method according to claim 22, wherein the non-aqueous solution comprises about 10 g/L to about 25 g/L of the metallization inhibitor.
 24. The method according to claim 23, wherein the non-aqueous solution comprises about 15 g/L to about 20 g/L of the metallization inhibitor.
 25. The method according to claim 13, wherein the non-aqueous solution is maintained at a temperature of between about 25° C. and about 75° C. during the time that the electroplating rack is immersed in the non-aqueous solution.
 26. The method according to claim 25, wherein the non-aqueous solution is maintained at a temperature of between about 35° C. and about 65° C. during the time that the electroplating rack is immersed in the non-aqueous solution.
 27. The method according to claim 13, wherein the electroplating rack is immersed in the non-aqueous solution for between about 1 minute and about 60 minutes.
 28. The method according to claim 27, wherein the electroplating rack is immersed in the non-aqueous solution for between about 2 minute and about 30 minutes.
 29. (canceled)
 30. The method according to claim 11, further comprising the steps of: a) activating the surface of the non-conductive substrates by immersing the electroplating rack with the non-conductive substrates mounted thereon into a solution comprising colloidal palladium/tin or ionic palladium; b) immersing the electroplating rack containing the etched and activated non-conductive substrates mounted thereon in an electroless metallization bath to electrolessly deposit metal thereon; and c) electroplating the non-conductive substrates to plate metal thereon, wherein the treated coated portion of electroplating rack remains free of the electrolessly deposited metal. 